Benefit agents, such as perfumes, silicones, waxes, flavors, vitamins and fabric softening agents, are expensive and generally less cost effective when employed at high levels in personal care compositions, cleaning compositions, and fabric care compositions. As a result, there is a desire to maximize the effectiveness of such benefit agents. One method of achieving such objective is to improve the delivery efficiency and active lifetime of the benefit agent. This can be achieved by providing the benefit agent as a component of a microcapsule.
Microcapsules are made either by supporting the benefit agent on a water-insoluble porous carrier or by encapsulating the benefit agent in a water-insoluble shell. In the latter category microencapsulates are made by precipitation and deposition of polymers at the interface, such as in coacervates, for example as disclosed in GB-A-O 751 600, U.S. Pat. No. 3,341,466 and EP-A-0 385 534, or other polymerisation routes such as interfacial condensation U.S. Pat. No. 3,577,515, US-A-2003/0125222, U.S. Pat. No. 6,020,066, W02003/101606, U.S. Pat. No. 5,066,419. A particularly useful means of encapsulation is using the melamine/urea-formaldehyde condensation reaction as described in U.S. Pat. No. 3,516,941, U.S. Pat. No. 5,066,419 and U.S. Pat. No. 5,154,842. Such capsules are made by first emulsifying a benefit agent in small droplets in a pre-condensate medium obtained by the reaction of melamine/urea and formaldehyde and then allowing the polymerisation reaction to proceed along with precipitation at the oil-water interface. The encapsulates ranging in size from a few micrometer to a millimeter are then obtained in a suspension form in an aqueous medium.
Microcapsules provide several benefits. They have the benefit of protecting the benefit agent from physical or chemical reactions with incompatible ingredients in the composition, volatilization or evaporation. Microcapsules have the further advantage in that they can deliver the benefit agent to the substrate and can be designed to rupture under desired conditions, such as when a fabric becomes dry. Microcapsules can be particularly effective in the delivery and preservation of perfumes. Perfumes can be delivered to and retained within the fabric by a microcapsule that only ruptures, and therefore releases the perfume, when the fabric is dry.
Preferred microcapsules have a core-in-shell architecture and comprise a shell of formaldehyde-containing resin. The Applicants have found, however, that when such microcapsules are formulated into a composition, regardless of the content of the core of the microcapsule, the composition containing said microcapsule becomes discoloured. Particularly problematic is a blue product discolouring to green. This is particularly problematic when the product is packaged in a transparent or translucent container. Discoloration appears to be dependent on microcapsule level and storage temperature. Higher storage temperature and/or higher concentration of microcapsule results in a product that discolours faster and with more colour depth.